Wounds and lesions can be caused by a variety of events, including surgery, traumatic injury, burns, abrasions and skin grafts. Healing of wounds may be difficult and may result in problems such as ulcers and septicemia. Of particular concern are chronic wounds, such as pressure sores and diabetic ulcers. The treatment of these conditions is of increasing importance as the population ages. The conventional cascade of biochemical processes which occurs in wound healing, involving hemostasis and inflammation, granulation tissue formation and reepithelization and remodeling, is disrupted in the case of chronic wounds due in part to the prolonged inflammatory response which occurs, and the release of destructive enzymes by inflammatory cells.
It has been recognized for some time that maintaining a moist environment can improve the rate of wound healing. Many products have been developed which provide this environment in order to increase the rate of repair of chronic wounds. The materials used in these dressings are biocompatible to some extent, and include polylactic acid, chitin, alginate derivatives and collagen. The response of these materials to wound exudates, and the biochemical environment that these materials provide are fundamental to their performance in the wound.
Commercially available dressings include various synthetic materials such as silicone compounds, nylon fabrics, or petrolatum gauzes and the like [A. J. Platt, A. Phipps and K. Judkins, A comparative study of silicone net dressing and paraffin gauze dressing in skin-grafted sites, Burns, 22(7), 1996, p. 543-545; Claudia Valenta and Barbara G. Auner, The use of polymers for dermal and transdermal delivery, European Journal of Pharmaceutics and Biopharmaceutics, 58(2), 2004, p. 279-289]. Whilst these conventional wound dressing materials are inexpensive and easily available, they generally have poor affinity with the wounded area, insufficient vapour permeability are ultimately unsatisfactory with regards to long term healing of chronic wounds [Marcel F. Jonkman, Izaäk Molenaar, Paul Nieuwenhuis, Peter Bruin and Albert J. Pennings, New method to assess the water vapour permeance of wound coverings, Biomaterials, 9(3), 1988, p. 263-267]. High-performance wound dressing materials are often derived from natural materials having properties similar to those of the patients' skin.
Wound dressing can be created using natural materials or through combination of synthetic materials and natural materials (JP# 47470/1988; Jen Ming Yang and Hao Tzu Lin, Properties of chitosan containing PP-g-AA-g-NIPAAm bigraft nonwoven fabric for wound dressing, Journal of Membrane Science, 243(1-2), 2004, p. 1-7). The use of wound dressings is an extremely important part of wound management and vital to achieve successful healing outcomes [Gordon Freedman, Hyacinth Entero and Harold Brem, Practical treatment of pain in patients with chronic wounds: pathogenesis-guided management, The American Journal of Surgery, 188(1), 2004, p. 31-35]. An optimum wound dressing protects the injured tissue, maintains a moist environment, is water permeable, maintains microbial control, delivers healing agents to the wound site, is easy to apply, does not require frequent changes and is non-toxic and non-antigenic.
Currently several forms of wound dressings materials are available commercially, including occlusive dressings, non-adherent dressings, absorbent dressings, and dressings in the form of sheets, foams, powders and gels. Attempts have been made to provide improved dressings, particularly for chronic wounds, that assist in the wound healing process by using biological materials such as cells and growth factors. To date, these biologicals have proven very costly due to factors such as manufacturing processes and storage and stability issues, and in addition they have shown minimal clinical relevance in accelerating the chronic wound healing process. Above all effective, wound management requires an understanding of the process of tissue repair and knowledge of the properties of the wound dressing materials. Only when these two factors are considered together can the process of dressing selection be undertaken in a rational and informed fashion.
Keratin proteins are present in a wide range of biological tissue, performing a structural role in skin, hair and other materials. Keratins extracted from hair have been shown to be a valuable component in wound dressings. U.S. Pat. No. 5,932,552 provides a biocompatible keratin material prepared by either reduction or oxidation for use as a component in wound care products. Those methods included in the art for the oxidation of keratins to create a polar group are harsh and degrading to the keratin, causing protein damage and loss of core physical characteristics arising from the protein amino acid composition and tertiary structure. In addition the oxidation processes used in the preparation of these materials are irreversible and the cysteic acid groups formed cannot be reconverted to cystine to perform a useful structural function. Those methods included in the art for reduction to create soluble proteins are conducted under harsh alkaline conditions that also cause damage to the protein and loss of the core physical characteristics of the keratin proteins.
The core components of keratin fibres, specifically the intermediate filament proteins and the matrix proteins present in wool and hair, play particular roles within the fibre which is reflected in their tertiary structure and amino acid composition. These same features can be capitalized upon to create materials with good physical properties and highly absorbing capacities when using purified forms of these proteins. In order to do this, methods used for isolating keratins need to be mild, to prevent protein damage, create cystine modifications that are reversible, to allow for reconstitution of tough materials through the creation of cystine bonds, and facilitate the isolation of specific keratin protein fractions from the keratin source. The present invention provides new materials for use in wound care products that are prepared according to these principles.